Home networking has become a recognizable retail term, and devices that a consumer can network "out of the box" now seem quite possible. That fairly recent state of affairs is due largely to standardization efforts in consumer electronics (CE) that leverage platforms from the information technology industry in enterprise environments, enhance or supplement them to accommodate entertainment and consumer expectations for QoS, and build on common methods or reference models across the platforms. These efforts include those by CEA, the UPnP (universal plug and play) Forum and IEEE (Ethernet and 1394).

In the CEA, home-networking standards are developed by the R7 committee. Several efforts are under way in R7 that are expected to culminate in comprehensive device and platform specifications for consumer networking, building on the ubiquitous Internet protocols and using two popular networking technologies that have emerged for interconnecting audio-video devices: IEEE 1394 and IEEE 802.3 Ethernet. R7.4 is updating CEA-851, the Versatile Home Network (VHN) standard, and R7.6 is releasing version 1 of CEA-2008, the Digital Entertainment Network Initiative (DENi) standard. While VHN uses 1394 and DENi uses Ethernet, both standards incorporate UPnP device specifications and use IP traffic.

R7.5 is also due to release two AV networking (AVN) standards this year: the CEA-2005 Audio-Video Networking Architecture, which includes an adapter to connect dissimilar networks (e.g., 1394 and Ethernet), and CEA-2007 QoS Priority Groups for Ethernet.

The AVN standards are necessary because the requirements of AV devices differ from those of traditional IT devices. Whereas IT device communications are "bursty" in nature, AV devices send continuous streams of data. The 1394 protocols are designed to handle AV streams with a guaranteed QoS, whereas Ethernet protocols offer best effort. While developing an architecture for AV networking, R7.5 recognized that Ethernet's method for dealing with QoS works better for the Internet and client-server models used in corporate IT networks than it would for multimedia networks. Whether a consumer wants to connect 1394 devices to an Ethernet network or simply to handle AV streams on an Ethernet network, a different QoS model is needed for AV on Ethernet, and it has to be one that allows legacy devices to coexist with new products.

Ethernet backbone

A possible scenario for future home networking involves both IT and AV devices, using a mix of 1394 and Ethernet connections. In this example, the "backbone" distribution network-that is, the connection to each room-is high-speed Ethernet. The computer and the media server connections are also Ethernet but may use slower Ethernet connections. Expansion hard disks for the media server use 1394, as do the AV devices. Another room might use a wireless IP connection to the backbone.

The CEA R7.5 AVN architecture subcommittee uses the term "adapter" to specify the conversion of 1394 and Ethernet protocols. The adapter functionality could be contained in wall plate modules, reside in a separate conversion box or reside in a CE device that has both 1394 and Ethernet connections.

The adapter must address a number of issues in the conversion of protocols between 1394 and Ethernet:

• Wireless connectivity. The connection of wireless technologies to a wired backbone presents a number of problems, including packet loss, low bit rates and differing access protocols.

• Clock synchronization. This is important for the uniform playback of the same media on multiple devices. An example is multiroom audio: Schemes must ensure that the selected music is rendered in each room at precisely the same time in order to eliminate echo.

• Media formats. The adapter must also understand various media formats for efficient decomposition and recomposition of packets transferred between Ethernet and 1394.

• Device discovery. In a home network, it is necessary to discover and control the connected devices through a common protocol. The R7.5 subcommittee chose UPnP v1.0 device specifications for that job. Ethernet and 1394 devices must implement UPnP v1.0, and legacy devices (either 1394- or Ethernet-based) that do not support UPnP discovery will require a proxy service to expose the devices as UPnP devices to the network.

• Isochronous transfers. The 1394 spec uses isochronous transfer protocols for AV data streams, but there is no isochronous transfer protocol on IP Ethernet. Thus the adapter must convert between 1394 isochronous protocols and Ethernet IP protocols. R7.5 is specifying a number of protocol conversion mechanisms, such as HTTP Get and RTP, that can be used, depending on the capabilities of the Ethernet network.

• Packet size. IP Ethernet and 1394 have different optimal packet sizes and transfer rates. For AV streams, 1394 uses small packets transferred at regular intervals of 125 microseconds. The nature of Ethernet dictates larger packets transferred in longer intervals. Further, there is a speed-matching problem: The native signaling rates of 1394 and Ethernet differ. (The typical 1394 rate is 400 Mbits/second; Ethernet typically achieves rates of 100 Mbits/s).

QoS is an area of particular importance for the adapter in bridging 1394's rigid QoS protocols, including reserved bandwidth, and Ethernet's best-effort access. Using the 802.1Q header extension, which includes a priority field, possibilities exist for "better than best-effort" Ethernet access. CEA-2007 QoS Priority Groups for Ethernet, currently under consideration in the CEA, uses the priority field in the 802.1Q header to allow three IP QoS models to coexist concurrently on Ethernet-based networks. The three supported models (types of service) are best effort (no QoS), prioritized QoS and parameterized QoS.

The use of priority to realize QoS is referred to simply as prioritized QoS. Using 802.1Q prioritized QoS on Ethernet networks, AV applications can specify a higher priority than data applications, allowing the AV application to have "first right" to the network. But if the total number of AV streams exceeds the bandwidth of the Ethernet, then all AV streams will suffer.

A parameterized QoS model involves reserving resources for the end-to-end path of the AV stream. Thus, when there is not enough bandwidth to support a new stream, that stream won't be started, and the existing streams will continue unaffected. Parameterized QoS is somewhat complicated, however, and not all companies agree that it is required for home- or consumer-grade networks.

The priority field is logically divided into four groups. Network management commands use the highest priority to ensure that network bandwidth and resources can be recovered. Parameterized QoS ensures that devices that have allocated resources throughout the network have first access to the network.

Prioritized QoS benefits from using priority to gain access to the network, but parameterized services still have a higher priority. Best effort is the lowest priority, and its traffic is restricted to the availability of the network after all higher-priority traffic has been sent. Legacy devices get best-effort access by default.

The collection of standards for integrated consumer networking currently under development in R7 is expected to be completed this year. For more information, go to www.ce.org.

Glen Stone is in the Network and Systems Architecture Division at Sony Corp.'s Platform Technology Center of America.

Virginia Williams is director of technology and standards at the Consumer Electronics Association.